1. Field of the Invention
The present invention relates to a bias source control circuit including stand-by means.
This application is related to an application entitled DEVICE FOR SETTING A BIAS SOURCE AT PARTIAL STAND-BY AND CONTROL CIRCUIT FOR SUCH A SOURCE and to an application entitled DEVICE FOR SETTING A BIAS SOURCE AT STAND-BY, both filed on even date herewith, and incorporated herein by reference.
2. Discussion of the Related Art
Stand-by devices are used to reduce power consumption in a circuit during periods of non-use by deactivating the bias source, without it being necessary to switch off the circuit. They are of particular interest for systems with an independent power supply, consisting of, for example, ordinary or rechargeable batteries, such as remote sensors. The role of such sensors is, for example, to transmit data to a control panel in the case of a change in the state of the sensor. In such devices, it is essential to limit the consumption of the sensor during periods when its state is stable. In order to do this, the bias source of its emission units is set at stand-by when the sensor is in a stable state for a predetermined time interval. This enables the power consumption of the device to be reduced during these periods. The bias source is restarted, or reactivated as soon as the stand-by control signal changes state, giving an indication that the sensor no longer is in a stable state.
A bias source start-up aid device is usually implanted in the control circuit, to allow the bias source to be started up. Such a device generally operates independently of the stand-by device, and it is only used when a voltage is applied to the circuit for the initial start-up of the bias source after its complete extinction, and is then electrically disconnected from the bias source. Conventionally, the bias source is thus never completely switched off during its stand-by periods. The existing stand-by devices reduce circuit consumption and maintain the bias source in its active state, otherwise the control circuit would no longer have means to restart the bias source, these means having been inhibited after a voltage has been applied to the circuit.
A drawback of these existing circuits is that they continue to consume power even during stand-by periods of the bias source. This consumption is due to the residual consumption of the source during its stand-by periods, and to that of the start-up aid device.
Additionally, there is a transient consumption at the switching of the circuit from a nominal operation state to a stand-by state of bias source 1. Indeed, such a control circuit conventionally includes a logic device including CMOS inverters. The role of the inverters is to produce a signal, which corresponds to a logic signal for the control circuit, from a stand-by control signal that is received by the control circuit. During the transition of the stand-by control signal between a state corresponding to non-stand-by to a state corresponding to stand-by, the current that flows through the inverters reaches a peak that falls following the fall of the stand-by control signal. Thus, useless power is consumed at the switching of the inverters.
Moreover, the stand-by control signal, although generally being a logic signal, frequently varies between two potentials that do not necessarily correspond to the bias source supply potentials. In this case, from the view-point of the bias source, the stand-by control signal is not a logic signal. As a consequence, a current flows through the logic device during the whole period when the bias source is deactivated, which results in a significant residual consumption of power. This consumption is all the more important as the difference between the low state potential of the stand-by control signal and the potential of the negative terminal of the supply voltage is important.
Such power consumptions reversibly affect the autonomy of independently supplied systems, but cannot be avoided in conventional circuits, particularly because the bias source cannot be totally switched off during stand-by periods, because it is necessary to be able to reactivate it.